If you've already got the DMT 4" hones (and I'm assuming these are the same ones used with the Aligner), I'd just go with the Aligner kit. You'll still need the stone holder/guide rod for those hones anyway, which is part of that kit. Your hones won't be adaptable to another system without it, UNLESS you use your 4" hones like small bench hones. Then, all you'd need is the clamp itself. You'd still need to figure out how best to support and/or elevate those small hones, to make them more user-friendly for bench-honing.
If you're curious about differences in the clamps themselves (Aligner, Lansky, Gatco), one particular thing I like about Lansky's latest-generation clamp is, it's better with small blades, such as those in traditional pocketknives. The Aligner clamp is generally easier to set up on somewhat larger blades, but really doesn't adapt well to small blades, without some shimming or similar rigging. The Gatco clamp has more angle settings than either of those, but also doesn't do as well with smaller blades (doesn't hold them securely, at least with the version I have). This used to be an issue with older versions of Lansky's clamp, but they very wisely improved theirs.
I also tend to prefer the Magna-Guide/Dia-Fold combo with the Aligner clamp. But, since you already have the 4" hones, it may be worth trying a minimal Aligner kit first (save a little $$). You may find it suits your needs just fine.